1. Field of the Invention
The present invention relates to a device for regenerating a picture signal by decoding it and, more particularly, to a device for regenerating digital picture data coded by compression and transmitted or stored by decoding while reducing distortions between nearby blocks which constitute the picture data.
2. Description of the Related Art
Generally, when picture data generated by an electronic still camera or similar digital picture data is stored in a memory or transmitted to a remote station, it is a common practice to code the picture data by compression for the purpose of reducing the amount of data. Among various conventional compression schemes, two-dimensional orthogonal transform is extensively used since it compresses picture data by a large ratio and causes a minimum of distortion ascribable to coding to occur in a picture.
The two-dimensional orthogonal transform type coding divides picture data into a predetermined number of blocks and transforms the picture data block by block. The transformed picture data have transform coefficients thereof compared with a predetermined threshold value, and the coefficients smaller than the threshold value are discarded. The transform coefficients greater than the threshold value are each divided by a particular quantizing step value, i.e., normalizing coefficient and thereby quantized or normalized by the step width. The normalized transform coefficients are coded by Huffman coding to produce compressed picture data. The compressed picture data is written to a memory or transmitted to a remote station.
To regenerate original picture data, the picture data compressed by the above procedure is decoded by Huffman decoding and then subjected to reverse normalization and reverse orthogonal transform. The problem with this kind of compressed picture data is that since the picture data has been divided into blocks and then subjected to orthogonal transform and coding block by block, the decoded picture data has distortions between nearby blocks, i.e. interblock distortions. Especially, the border or edge between nearby blocks is conspicuous in relatively monotonous portions of a picture, which lowers the quality of a reproduced image.